Lithium air battery

ABSTRACT

Provided is a lithium air battery in which a catalyst layer of a cathode contacting an electrolyte and using oxygen in the air as an active material is coupled to a membrane through which lithium ions pass, such that even though charge and discharge of the battery is repeated, the catalyst layer may not be detached, and a microporous polyolefin-based film is applied to the battery, such that a water-based electrolyte solvent may be prevented from being evaporated, thereby preventing performance deterioration due to repetition of the charge and discharge of the lithium air battery, and extending life span.

TECHNICAL FIELD

The present invention relates to a lithium air battery, and morespecifically, to a lithium air battery capable of preventing performancedeterioration due to repetition of charge and discharge of the batteryand extending life span.

BACKGROUND

Recently, in accordance with an increase in carbon dioxide emission dueto consumption of fossil fuel, a rapid change of crude oil price, andthe like, development of a technology of converting from gasoline anddiesel oil to an electric energy as an energy source of automobile hasbeen spotlighted. Commercialization of an electric automobile hasprogressed, and for a long-distance driving, a lithium ion battery whichis a storage battery has been required to have large capacitance andhigh energy densification. However, the current lithium ion battery hasa limitation in battery capacitance, thereby having difficulty in a longdistance driving. Therefore, a lithium air battery having largercapacitance and higher energy density in theory as compared to thelithium ion battery has been spotlighted.

In general, the lithium air battery includes an anode capable ofadsorbing and emitting lithium ion, a cathode including anoxidation-reduction catalyst of oxygen using oxygen in the air as acathode active material, wherein a lithium ion conductive medium isprovided between the cathode and the anode. That is, the lithium airbattery, which is a battery having the cathode using oxygen in the airas the active material, is a battery capable of charging and dischargingthe battery by performing an oxidation-reduction reaction of oxygen inthe cathode.

The lithium air battery has a theoretical energy density of 3000 Wh/kgor more, which corresponds to an energy density approximately 10 timeslarger than that of the lithium ion battery. In addition, the lithiumair battery is environment-friendly and may provide more improvedstability than that of the lithium ion battery.

However, in the existing lithium air battery, due to repetition ofcharge and discharge of the battery, a catalyst layer of the cathode isdetached and a water-based electrolyte solvent used between a solidelectrolyte and porous air-cathode is evaporated, such that performanceof the lithium air battery may be deteriorated and life span may bereduced.

As the related art document regarding the above-description, US PatentApplication Publication No. 2012/0028164 entitled “lithium air battery”is disclosed.

RELATED ART DOCUMENT

(Patent Document 1) US Patent Application Publication No. 2012/0028164A1 (Feb. 2, 2012)

SUMMARY

An embodiment of the present invention is directed to providing alithium air battery capable of not detaching a catalyst layerconfiguring a cathode thereof but preventing a water-based electrolytesolvent from being evaporated, thereby improving durability, preventingperformance deterioration, and extending life span.

In one general aspect, a lithium air battery includes: a first electrodepart including a lithium metal; a second electrode part including a gasdiffusion layer of which one side contacts an air, a catalyst layerformed at the other side of the gas diffusion layer, and a membranecoupled to the catalyst layer so that lithium ions pass therethrough,and spaced apart from the first electrode part; and an electrolyte partprovided between the first electrode part and the second electrode part.

The electrolyte part may include a separator closely adhered on one sideof the first electrode part and containing an organic-based electrolyte,a solid electrolyte closely adhered on one side of the separator, and awater-based electrolyte provided between the solid electrolyte and thesecond electrode part.

The second electrode part may further include a microporouspolyolefin-based film coupled on one side of the gas diffusion layer.

The lithium air battery may further include: a housing part including afirst housing provided with a space part having an open upper side, anda second housing having an air accommodation part disposed at an upperportion of the first housing, sealing the space part of the firsthousing, and having an open lower side, and ventilation holes formedtherein to communicate with the air accommodation part, wherein thefirst electrode part is accommodated into the space part of the firsthousing, the second electrode part is coupled to a lower side of the airaccommodation part of the second housing to be spaced apart from thefirst electrode part and has the gas diffusion layer disposed on anupper side thereof and the membrane disposed on a lower side thereof,and the electrolyte part is provided in the space part of the firsthousing to be provided between the first electrode part and the secondelectrode part.

The electrolyte part may include a separator closely adhered on an upperside of the first electrode part and containing an organic-basedelectrolyte, a solid electrolyte closely adhered on an upper side of theseparator, a water-based electrolyte provided between the solidelectrolyte and the second electrode part, and an accommodation bodyprovided on an upper side of the solid electrolyte and having anaccommodation hole vertically penetrating therethrough, and theaccommodation body may be disposed so that the solid electrolyte, theseparator, and the first electrode part are closely adhered to the spacepart.

The housing part may further include a third housing interposed betweenthe first housing and the second housing and having a fixing holevertically penetrating therethrough so that the second electrode part isfixed to the fixing hole.

The membrane may be a porous membrane containing a sulfonic acid group.

The membrane may be made of a polyperfluorosulfonic acid (PFSA) resinhaving a porous material.

The membrane may be closely adhered to the catalyst layer by heating andpressing the PFSA resin or by a dip-coating method using a PFSA resinsolution.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention relates to a lithium air battery in which acatalyst layer of a cathode contacting an electrolyte and using oxygenin the air as an active material is coupled to the membrane throughwhich the lithium ions pass, such that even though charge and dischargeof the battery is repeated, the catalyst layer may not be detached, andmicroporous polyolefin-based film is applied to the battery, such that awater-based electrolyte solvent may be prevented from being evaporated,thereby preventing performance deterioration due to repetition of thecharge and discharge of the lithium air battery, and extending lifespan.

FIG. 1 is a conceptual diagram showing a lithium air battery of thepresent invention;

FIGS. 2 and 3 are an assembled perspective view and an explodedperspective view of a lithium air battery according to an embodiment ofthe present invention, respectively;

FIG. 4 is a cross sectional view taken along line AA′ of FIG. 2;

FIG. 5 is a photograph showing a surface of an initial state of acatalyst layer containing platinum and a binder mixed thereto;

FIG. 6 is a photograph showing the catalyst layer of FIG. 5 afterrepetition of charge and discharge cycles 200 times;

FIG. 7 is a photograph showing a cross-section of the initial state ofcatalyst layer containing platinum and the binder mixed thereto and angas diffusion layer;

FIG. 8 is a photograph showing a cross-section of the catalyst layer ofFIG. 7 having a state in which particles therein are detached afterrepetition of the charge and discharge cycles 200 times;

FIG. 9 is a photograph showing a surface of a microporouspolyolefin-based film;

FIG. 10 is a photograph showing a cross-section of the microporouspolyolefin-based film of FIG. 9;

FIG. 11 is a graph showing a charge and discharge cycle of a lithium airbattery including porous air-cathode without the microporouspolyolefin-based film and Nafion membrane;

FIG. 12 is a graph showing a charge and discharge cycle of a lithium airbattery including porous air-cathode to which Nafion membrane is notapplied but the microporous polyolefin-based film is applied;

FIG. 13 is a graph showing a charge and discharge cycle of a lithium airbattery (sample 1) including porous air-cathode to which both of Nafionmembrane and the microporous polyolefin-based film are applied;

FIG. 14 is a graph showing charge and discharge energy of sample 1;

FIG. 15 is a graph showing charge and discharge energy efficiency ofsample 1;

FIG. 16 is a graph showing a charge and discharge cycle of a lithium airbattery (sample 2) including porous air-cathode to which both of Nafionmembrane and the microporous polyolefin-based film are applied;

FIG. 17 is a graph showing charge and discharge energy of sample 2;

FIG. 18 is a graph showing charge and discharge energy efficiency ofsample 2;

FIG. 19 is a photograph showing comparison of a discoloration degreebetween a water-based electrolyte in a lithium air battery includingporous air-cathode without Nafion membrane and a water-based electrolytein a lithium air battery including porous air-cathode with Nafionmembrane, after tens of cycles;

FIG. 20 is a graph showing the charge and discharge cycle at 421 timesof a lithium air battery including porous air-cathode to which both ofNafion membrane and the microporous polyolefin-based film are applied;

FIG. 21 is a graph showing charge and discharge energy of the lithiumair battery of FIG. 20; and

FIG. 22 is a graph showing charge and discharge energy efficiency of thelithium air battery of FIG. 20.

[Detailed Description of Main Elements] 1000: Lithium Air Battery  100:Housing Part  110: First Housing  111: Space Part 112: Coupling Hole 120: Second Housing 121: Ventilation Hole  122: Air Accommodation Part 127: First Fixing Part  128: First Coupling Part  130: Third Housing131: Fixing Hole  132: Second Fixing Part 133: Second Coupling Part 134: Through Hole  200: First Electrode Part  210: Lithium Metal 220:Current Collector  300: Second Electrode Part  311: Gas Diffusion Layer312: Catalyst Layer  313: Membrane  314: Microporous Polyolefin-basedFilm  400: Electrolyte Part  410: Separator (Organic-based Electrolyte) 420: Solid Electrolyte  430: Accommodation Body 431: Accommodation Hole 440: First Sealing Part 450: Water-based Electrolyte

DETAILED DESCRIPTION OF EMBODIMENTS

The advantages, features and aspects of the present invention willbecome apparent from the following description of the embodiments withreference to the accompanying drawings, which is set forth hereinafter.The present invention may, however, be embodied in different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the presentinvention to those skilled in the art. The terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be limiting of example embodiments. As used herein, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Hereinafter, a lithium air battery according to the present inventionwill be described in detail with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram showing a lithium air battery of thepresent invention, and FIGS. 2 and 3 are an assembled perspective viewand an exploded perspective view of a lithium air battery according toan embodiment of the present invention, respectively.

As shown in the drawings, the lithium air battery 1000 according to thepresent invention includes: a first electrode part 200 including alithium metal 210; a second electrode part 300 including a gas diffusionlayer 311 of which one side contacts an air, a catalyst layer 312 formedat the other side of the gas diffusion layer 311, and a membrane 313coupled to the catalyst layer 312 so that lithium ions passtherethrough, and spaced apart from the first electrode part 200; and anelectrolyte part 400 provided between the first electrode part 200 andthe second electrode part 300.

First, the lithium air battery 1000 of the present invention largelyconsists of the first electrode part 200, the second electrode part 300,and the electrolyte part 400.

The first electrode part 200 may include a lithium metal 210 capable ofstoring and emitting the lithium ions, and may further include a binder.Examples of the lithium metal 210 may include a lithium metal, an alloybased on the lithium metal, a lithium intercalating compound, and thelike, and among them, a lithium alloy is preferred in order to improvedurability with respect to moisture, and the like. Examples of thebinder may include polyvinylidene fluoride (PVdF),polytetrafluoroethylene (PTFE), and the like, and a content, of thebinder is not specifically limited, but may be 30 wt % or less, and morespecifically, 1 to 10 wt %.

The second electrode part 300 includes the gas diffusion layer (GDL) 311of which one side contacts an air, the catalyst layer 312, and themembrane 313, and is spaced apart from the first electrode part 200.Here, as shown in FIG. 1, the second electrode part 300 includes themembrane 313 disposed on a surface facing the first electrode part 200and is formed by forming the catalyst layer 312 on one side of the gasdiffusion layer 311, and coupling the membrane 313 to one side of thecatalyst layer 312. Then, air is diffused through the gas diffusionlayer 311, such that an oxidation-reduction reaction between lithiumions and oxygen in the air is generated in the catalyst layer 312.

Here, the second electrode part 300 may use oxygen in the air as anactive material and may contain conductive materials having poresthrough which oxygen and lithium ions pass, and the catalyst layer 312may be formed by mixing platinum (Pt) and binder and applying or coatingthe mixture. That is, the catalyst layer 312 may be formed by mixing thecatalyst, the conductive material, and the binder, performing apress-molding process on the gas diffusion layer (or carbon paper) 311,or by mixing the catalyst, the conductive material, and the binder andthen dissolving or dispersing the mixture into an organic solvent suchas acetone, methyl ethyl ketone, N-methyl-2-pyrrolidone, or the like, tothereby prepare a slurry, applying′ the prepared slurry on the gasdiffusion layer 311 by gravure coating, blade coating, comma coating,dip coating methods and dispensing an organic solvent, followed bypressing.

In addition, as the conductive material, carbon materials, conductivefibers such as metal fiber, and the like, metal powder such as copper,silver, nickel, aluminum, and the like, organic conductive materialssuch as polyphenylene derivatives, and the like, may be used. As thecarbon material, carbon black, graphite, activated carbon, carbonnanotube, carbon fiber, and the like, may be used, and mesoporous carbonobtained by firing synthetic resin containing an aromatic ring compound,petroleum pitch, and the like, may be used.

The electrolyte part 400 is provided between the first electrode part200 and the second electrode part 300, such that the lithium ions aremovable.

Therefore, the first electrode part 200 including the lithium metal 210becomes an anode, and the second electrode part 300 becomes a cathode,and the electrolyte part 400 is provided between the first electrodepart 200 and the second electrode part 300, thereby configuring thelithium air battery 1000.

Here, in the lithium air battery 1000, at the time of charge anddischarge the battery, air is diffused through the gas diffusion layer311 of the second electrode part 300, such that the oxidation-reductionreaction between oxygen in the air and the lithium ions is generated inthe catalyst layer 312, and when the charge and discharge is repeated,crack may occur in the catalyst layer 312, such that particles(platinum, binder, and conductive materials) forming the catalyst layer312 may be detached from the gas diffusion layer 311 toward theelectrolyte part 400. Therefore, performance of the lithium air batterymay be deteriorated and life span thereof may be reduced.

Here, in the lithium air battery 1000 of the present invention, thecatalyst layer 312 of the second electrode part 300 is coupled to themembrane 313 allowing the lithium ions to be passed therethrough andpreventing the particles of the catalyst layer 312 from being detached,such that even though the charge and discharge of the battery isrepeated, performance deterioration may be prevented and life span maybe extended.

FIGS. 5 and 6 are scanning electron microscope (SEM) photographs showingeach surface of catalyst layers containing platinum and a binder mixedthereto between an initial state and after repetition of charge anddischarge cycles 200 times, respectively, FIGS. 7 and 8 are scanningelectron microscope (SEM) photographs showing each cross-section of thegas diffusion layer and the catalyst layer between an initial state andafter repetition of the charge and discharge cycles 200 times.

That is, it may be appreciated from FIG. 6 that after repetition of thecharge and discharge, cracks occur in the catalyst layer 312, andtherefore, from FIG. 8 that a portion (shown by oval circle) of thecatalyst layer 312 is detached out from the gas diffusion layer 311,which may be appreciated from the following Table 1 that platinumcatalyst is detached from the catalyst layer due to repetition of thecharge and discharge even in a content of the platinum (Pt) catalystincorporated into the electrolyte part measured by inductively coupledplasma automic emission spectroscopy (ICP).

The following Table 1 shows a mass (mg/kg) per unit weight of platinumcontained in the water-based electrolyte after repeating the charge anddischarge of lithium air batteries in which platinum mass fractions ofthe catalyst layer 312 are 10 wt % and 40 wt %, respectively and thenperforming an analysis by ICP.

TABLE 1 Water-based Electrolyte Water-based Electrolyte Catalyst(Platinum 10 wt %) (Platinum 40 wt %) Platinum (Pt) 33.7 51.1

Therefore, according to the present invention, the membrane 313 coupledto the catalyst layer 312 may prevent the catalyst layer 312 from beingdetached, such that performance deterioration of the lithium air batterymay be prevented and life span thereof may be extended.

In addition, the electrolyte part 400 may include a separator 410closely adhered on one side of the first electrode part 200 andcontaining an organic-based electrolyte, a solid electrolyte 420 closelyadhered on one side of the separator 410, and a water-based electrolyte450 provided between the solid electrolyte 420 and the second electrodepart 300.

Therefore, electrochemical properties and charge and dischargeperformance of the lithium air battery may be improved. Here, since themembrane 313 is disposed between the water-based electrolyte 450 and thecatalyst layer 312 of the second electrode part 300 to be coupled to thecatalyst layer 312, detachment of the catalyst layer 312 according tothe repetition of the charge and discharge is prevented, such thatparticles of the catalyst layer 312 may be prevented from beingincorporated into the water-based electrolyte 450.

Herein, an organic based electrolyte, the solid electrolyte 420, and thewater-based electrolyte 450 will be described in more detail in thelithium air battery according to the embodiment of the presentinvention.

In addition, the second electrode part 300 further includes amicroporous polyolefin-based film 314 coupled on one side of the gasdiffusion layer 311.

That is, the microporous polyolefin-based film 314 is coupled on oneside of the gas diffusion layer 311 to thereby suppress the water-basedelectrolyte 450 solvent from being evaporated, such that even though thecharge and discharge of the lithium air battery is repeated, performancedeterioration thereof may be prevented and life span thereof may beextended.

In addition, the lithium air battery 1000 according to the embodiment ofthe present invention includes a housing part 100 including a firsthousing 110 provided with a space part 111 having an open upper side,and a second housing 120 having an air accommodation part 122 disposedat an upper portion of the first housing 110, sealing the space part 111of the first housing 110, and having an open lower side and ventilationholes 121 formed therein to communicate with the air accommodation part122, the first electrode part 200 including the lithium metal 210accommodated into the space part 111 of the first housing 110; thesecond electrode part 300 coupled to a lower side of the airaccommodation part 122 of the second housing 120 to be spaced apart fromthe first electrode part 200, and having the gas diffusion layer 311disposed on an upper side thereof, the catalyst layer 312 disposed on alower side of the gas diffusion layer 311, and the membrane 313 disposedon a lower side of the catalyst layer 312 to allow lithium ions to passtherethrough; and the electrolyte part 400 provided in the space part111 of the first housing 110 and provided between the first electrodepart 200 and the second electrode part 300.

That is, as shown in FIGS. 2 to 4, the lithium air battery 1000according to the embodiment of the present invention largely includesthe first electrode part 200, the second electrode part 300, and theelectrolyte part 400 in the housing part 100.

The housing part 100 includes the first housing 110 and the secondhousing 120. The first housing 110 has a disc shape and includes thespace part 111 formed therein, wherein the space part 111 is formed sothat an upper side thereof is open. In addition, the second housing 120also has a disc shape and is disposed on an upper portion of the firsthousing 110 and coupled so as to seal the space part 111 of the firsthousing 110. Here, the second housing 120 includes the air accommodationpart 122 formed on a lower side thereof and includes ventilation holes121 so as to communicate with the air accommodation part 122, such thatexternal air may flow into the air accommodation part 122 or may flowout to the air accommodation part 122, through the ventilation holes121. The number of ventilation holes 121 may be one or plural, whereinthe ventilation hole 121 may have various shapes so that air flows intothe air accommodation part 122 and or flows out to the air accommodationpart 122.

In addition, the second housing 120 has first fixing parts 127 formed atone side thereof to be coupled to the first housing 110, wherein firstcoupling parts 128 are inserted into the first fixing parts 127, suchthat the first housing 110 may be coupled to the second housing 120. Thefirst fixing part 127 of the second housing 120 according to a firstembodiment of the present invention is formed of a through hole, thefirst coupling part 128 is formed of a bolt, the first housing 110includes a coupling hole 112 as a female screw formed at a positioncorresponding to the first fixing part 127, such that the first couplingpart 128 is coupled to the coupling hole 112 by penetrating through thefirst fixing part 127, whereby the first housing 110 and the secondhousing 120 may be coupled to each other. Here, the first housing 110and the second housing 120 may be coupled in various schemes such asfit, welding, riveting, and the like, in addition to screw connection.

The first electrode part 200 includes a lithium metal 210, and thelithium metal 210 is accommodated into the space part 111 of the firsthousing 110.

The second electrode part 300 is coupled to the second housing 120 so asto seal the open lower side of the air accommodation part 122 of thesecond housing 120, and includes the gas diffusion layer 311 positionedat an upper side thereof and the catalyst layer 312 positioned at alower side thereof, wherein the lower side of the catalyst layer 312 maybe coupled to the membrane 313. Therefore, air accommodated into the airaccommodation part 122 is diffused through the gas diffusion layer 311,such that an oxidation-reduction reaction between lithium ions andoxygen in the air may be generated in the catalyst layer 312.

The electrolyte part 400 may be provided in the space part 111 of thefirst housing 110, and may be disposed on the upper portion of the firstelectrode part 200. The electrolyte part 400 is provided between thefirst electrode part 200 and the second electrode part 300, such thatthe lithium ions are movable.

That is, the first electrode part 200 including the lithium metal 210becomes an anode, and the second electrode part 300 becomes a cathode,and the electrolyte part 400 is provided between the first electrodepart 200 and the second electrode part 300, thereby configuring thelithium air battery 1000.

Therefore, in the lithium air battery 1000 according to an embodiment ofthe present invention, even though the charge and discharge of thebattery is repeated, the membrane 313 coupled to the lower side of thecatalyst layer 312 of the second electrode part 300 may prevent theparticles of the catalyst layer 312 from being detached toward theelectrolyte part 400, such that performance deterioration of the lithiumair battery may be prevented and life span thereof may be extended.

Here, the electrolyte part 400 may include a separator 410 closelyadhered on an upper side of the first electrode part 200 and containingan organic-based electrolyte, a solid electrolyte 420 closely adhered onan upper side of the separator 410, and a water-based electrolyte 450provided between the solid electrolyte 420 and the second electrode part300. Therefore, electrochemical properties and charge and dischargeperformance of the lithium air battery may be improved.

In addition, the second electrode part 300 may further include themicroporous polyolefin-based film 314 coupled to an upper side of thegas diffusion layer 311, wherein the microporous polyolefin-based film314 may prevent the water-based electrolyte 450 solvent from beingevaporated. In addition, since the microporous polyolefin-basedmicroporous film has extremely small size (about 10 nm) of pores and ahydrophobic property, evaporation of moisture which is the water-basedelectrolyte 450 solvent may be significantly suppressed.

Further, the electrolyte part 400 further includes an accommodation body430 provided on an upper side of the solid electrolyte 420 and having anaccommodation hole 431 vertically penetrating therethrough, and theaccommodation body is disposed so that the solid electrolyte 420, theseparator 410, and the first electrode part 200 are closely adhered tothe space part.

That is, as shown in FIG. 4, an upper edge part of the accommodationbody 430 is pressed down by the second housing 120, and the solidelectrolyte 420, the separator 410, and the first electrode part 200 maybe closely adhered onto bottom surface of the space part 111 due to theaccommodation body 430. Here, the accommodation body 430 has theaccommodation hole 431 formed in the center portion thereof so as tovertically penetrate therethrough, such that the water-based electrolyte450 contacts the solid electrolyte 420 through the accommodation hole431, whereby lithium ions may be movable.

Therefore, the lithium air battery 1000 according to an embodiment ofthe present invention has decreased contact resistance among theelectrolyte part 400, the first electrode part 200, and the firsthousing 110, such that efficiency and performance of the lithium airbattery may be improved, and life span thereof may be extended.

Here, a current collector 220 having a net shape may be provided on alower side of the lithium metal 210, such that the lithium metal 210,the electrolyte part 400, and the first housing 110 accommodated intothe space part 111 of the first housing 110, wherein the currentcollector 220 has a flexible net shape, such that the lithium metal 210and the electrolyte part 400 may contact each other so that the reactionis favorably performed. That is, the current collector 220, the lithiummetal 210, and the electrolyte part 400 accommodated into the space part111 of the first housing 110 may be closely adhered to each other by thecoupling of the second housing 120 to thereby significantly decrease thecontact resistance. In addition, the current collector 220 may be madeof copper, stainless, nickel, and the like.

Further, the electrolyte part 400 may further include a first sealingpart 440 allowing the first electrode part 200 to be accommodated intothe space part 111 so as to seal the space part 111.

The first sealing part 440 is interposed between edge parts of theelectrolyte part 400, and then due to the coupling of the first housing110 and the second housing 120, the first electrode part 200 is closedin the space part 111 by the electrolyte part 400 and the first sealingpart 440. That is, since the water-based electrolyte 450 is not allowedto flow into the first electrode part 200, corrosion of the lithiummetal 210 may be prevented, such that performance and life span of thelithium air battery may be improved.

Here, as shown in the drawings, the first sealing part 440 such asO-ring may be formed at a lower side edge part of the solid electrolyte420 and an upper side edge part of the accommodation body 430, of theelectrolyte part 400, respectively, to thereby improve sealing strengthfor sealing the first electrode part 200 into the space part 111. Inaddition, the separator 410 containing an organic electrolyte may alsobe sealed by the solid electrolyte 420 and the first sealing part 440.

Further, the housing part 100 may further include a third housing 130interposed between the first housing 110 and the second housing 120 andhaving a fixing hole 131 vertically penetrating therethrough so that thesecond electrode part 300 is fixed to the fixing hole 131.

That is, as shown in FIGS. 3 and 4, the third housing 130 is interposedbetween the first housing 110 and the second housing 120 and closelyadhered thereto. Here, the first electrode part 200 and the electrolytepart 400 are accommodated into the space part 111 of the first housing110 and the third housing 130 is coupled thereto from an upper sidethereof, such that the electrolyte part 400, the first electrode part200, and the bottom surface of the space part 111 of the first housing110 may be coupled to each other so as to be closely adhered, and thefirst housing 110 and the third housing 130 may perform screw-connectionbetween the second coupling part 133 formed of a bolt and the couplinghole 112 having female screw thread formed in the first housing 110.Here, the second fixing part 132 formed of the through hole throughwhich the second coupling part 133 penetrates may be formed in the thirdhousing 130, wherein the second fixing part 132 has an inclined upperside, the second coupling part 133 is formed of a flat headed bolt, suchthat an upper side head part of the second coupling part 133 does notprotrude upwardly than an upper surface of the third housing 130,whereby the second housing 120 may be easily closely adhered and coupledto the upper side of the third housing 130.

Then, the second housing 120 is closely adhered to the upper side of thethird housing 130 and the through-hole 134 is formed in the thirdhousing 130, such that the first coupling part 128 may penetrate throughthe first fixing part 127 and the through-hole 134 to performscrew-connection to the through-hole 112 of the first housing 110.

Here, an edge of the second electrode part 300 is closely adhered andfixed between the upper side edge part of the fixing hole 131 formed inthe third housing 130 and the second housing 120. In this case, as shownin the drawings, the upper side edge part of the fixing hole 131 may beinclined, and may have a step, such that the edge of the secondelectrode part 300 may be positioned at the step and fixed thereto. Inaddition, the water-based electrolyte 450 may be accommodated into thefixing hole 131, such that ions may be moved between the first electrodepart 200 and the second electrode part 300.

Therefore, the first housing 110, the second housing 120, and the thirdhousing 130 may be tightly coupled to each other to be closely adhered,adhesion strength between the first electrode part 200 and theelectrolyte part 400 may be improved, and the second electrode part 300may be easily coupled to the fixing hole and fixed thereto.

That is, the lithium air battery 1000 according to the embodiment of thepresent invention includes the housing part 100 having the first housing110, the second housing 120, and the third housing 130, such thatsealing property may be more excellent and durability may be improved ascompared to the existing lithium air battery having an open upperportion and a large space part formed therein.

Further, the membrane 313 may be a porous membrane containing a sulfonicacid group, more preferably, may be made of a polyperfluorosulfonic acid(PFSA) resin having a porous material. In addition, the membrane 313 maybe closely adhered to the catalyst layer by heating and pressing thePFSA resin. Further, the membrane 313 may be formed by a dip-coatingmethod using a PFSA resin solution. The PFSA membrane has a proton (H⁺,hydrogen ion)-conductivity (0.1 S/cm) and consists of hydrophilicsulfonyl group and hydrophobic fluorinated backbones in view of amolecular structure. Therefore, the membrane has a hydrophilic propertyand the proton-conductivity property to pass through Li⁺ ions and absorbwater required for a reaction with oxygen and water, thereby makingfunction of lithium-air smooth, which is appropriate for protection ofplatinum (Pt) catalyst layer according to an object of the presentinvention.

That is, the membrane 313 may be made of a material in which particlesof the catalyst layer 312 are capable of being prevented from beingdetached, and lithium ions are movable, which is the most preferred inview of performance of the lithium air battery.

In addition, the membrane 313 may be closely adhered to the catalystlayer 312 by performing a heating process and a pressing process. Thatis, the membrane 313 is heated and pressed by a high temperature on thecatalyst layer 312, such that coupling strength between the catalystlayer 312 and the membrane 313 may be improved, thereby definitelyblocking detachment of the particles of the catalyst layer 312 due tothe repetition of the charge and discharge of the battery.

In addition, herein, the water-based electrolyte 450 may be used bydissolving lithium acetate dihydrate (C₂H₃LiO₂, Sigma-Aldrich), lithiumchloride (LiCl, Sigma-Aldrich), lithium hydroxide (LiOH, Sigma-Aldrich)salts into D.I. water at a concentration of 1 mole. The water-basedelectrolyte 450 may be selected from an ionic liquid, that is, acompound represented by the following Chemical Formula 1 and mixturesthereof.X⁺Y⁻  [Chemical Formula 1]

[in Chemical Formula 1 above,

X⁺ is a imidazolium ion, a pyrazolinium ion, a pyridinium ion, apyrolidium ion, an ammonium ion, a phosphonium or a sulfonium ion; Y⁻ is(CF₃SO₂)₂N⁻, (FSO₂)SN⁻, BF₄ ⁻, PF₆ ⁻, AlCl₄ ⁻, halogen⁻, CH₃CO₂ ⁻,CF₃CO₂ ⁻, CH₃SO₄ ⁻, CF₃SO₃ ⁻, (CF₃SO₂)N⁻, NO₃ ⁻, SbF₆ ⁻, MePhSO₃ ⁻,(CF₃SO₂)₃C⁻, or (R″)₂PO₂ ⁻ (wherein R″ is C1-C5 alkyl).]

In Chemical Formula 1 above, cation (X⁺) may be exemplified by thefollowing Table 2:

TABLE 2 Cation (X⁺⁾ Structural Formula   Imidazolium Ion

Pyridinium Ion

Phosphonium Ion

Pyrazolium Ion

Pyrrolidium Ion

Ammonium Ion

Sulfonium Ion

In Table 2 above, R¹ to R²⁰ and R are each (C1-C20) alkyl, (C2-C20)alkenyl or (C2-C20) alkynyl, and wherein the alkyl, alkenyl and alkynylmay be further substituted with at least one selected from hydroxy,amino, —SO₃H, —COOH, (C1-C5)alkyl, (C1-C5)alkoxy, Si(R²¹)(R²²)(R²³)(R²¹,R²² and R²³ are each independently hydrogen or (C1-C5)alkyl,(C1-C5)alkoxy).

In Chemical Formula 1 above, anion (Y⁻) may be exemplified by thefollowing Table 3:

TABLE 3 Anion (Y⁻) Name of Anion BF₄ ⁻ tetrafluoroborate PF₆ ⁻hexafluorophosphate AlCl₄ ⁻ aluminium chloride X⁻ Halogen⁻ CH₃CO₂ ⁻acetate CF₃CO₂ ⁻ trifluoroacetate CH₃SO₄ ⁻ methylsulfate CF₃SO₃ ⁻trifluoromethylsulfate (CF₃SO₂)N⁻ bis[(trifluoromethyl)sulfonyl] amideNO₃ ⁻ nitrate SbF₆ ⁻ hexafluoroanimonate (FSO₂)₂N⁻Bis[fluorosulfonyl]imide MePhSO₃ ⁻ tosylate (CF₃SO₂)₂N⁻bis(trifluoromethylsulfo- nyl)imide (CF₃SO₂)₃C⁻tris(trifluoromethylsulfonyl) methide (OR)₂PO₂ ⁻ dialkyl phosphate

Examples of the water-based electrolyte may include 1-methyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazoliumbis(trifluoromethanesulfonyl)imide, 1-methyl-3-allylimidazoliumbis(trifluoromethanesulfonyl)imide, 1-methyl-3-ethylimidazoliumbis(fluorosulfonyl)imide, 1-methyl-3-propylimidazoliumbis(fluorosulfonyl)imide, 1-methyl-3-allylimidazoliumbis(fluorosulfonyl)imide, 1-methyl-1-propyl pyrolidiumbis(trifluoromethanesulfonyl)imide, 1-methyl-1-allyl pyrolidiumbis(trifluoromethanesulfonyl)imide, 1-methyl-1-propyl pyrolidium(fluorosulfonyl)imide, 1-methyl-1-allyl pyrolidium(fluorosulfonyl)imide, 1-butyl-3-methylimidazoliumchloride,1-butyl-3-methylimidazolium dibutylphosphate,1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazoliumhexafluoroantimonate, 1-butyl-3-methylimidazolium hexafluorophosphate,1-butyl-3-methylimidazolium hydrogencarbonate,1-butyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazoliummethylsulfate, 1-butyl-3-methylimidazolium tetrachloroaluminate,1-butyl-3-methylimidazolium tetrachloroborate,1-butyl-3-methylimidazolium thiocyanate, 1-dodecyl-3-methylimidazoliumiodide, 1-ethyl-2,3-dimethylimidazolium chloride,1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazoliumchloride, 1-ethyl-3-methylimidazolium hexafluorophosphate,1-ethyl-3-methylimidazolium tetrafluoroborate,1-hexyl-3-methylimidazolium tetrafluoroborate, 1-butyl-4-methylpyridiumchloride, 1-butyl-4-methylpyridium tetrafluoroborate,1-butyl-4-methylpyridium hexafluorophosphate,benzyldimethyltetradecylammonium chloride, tetraheptylammonium chloride,tetrakis(decyl)ammonium bromide, tributylmethylammonium chloride,tetrahexylammonium iodide, tetrabutylphosphonium chloride,tetrabutylphosphonium tetrafluoroborate, triisobutylmethylphosphoniumtosylate 1-butyl-1-methylpyrrolidinium, 1-butyl-1-methylpyrrolidiumbromide, 1-butyl-1-methylpyrrolidium tetrafluoroborate,1-aryl-3-methylimidazolium bromide, 1-aryl-3-methylimidazolium chloride,1-benzyl-3-methylimidazolium hexafluorophosphate,1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide,1-butyl-3-methylimidazolium dibutyl phosphate,1-(3-cyanopropyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)amide,1,3-dimethylimidazolium dimethyl phosphate,1-ethyl-2,3-dimethylimidazolium ethyl sulfate, and the like, andpreferably, 1-ethyl-3-methylimidazolium aluminum chloride,1-butyl-4-methylpyridium hexafluorophosphate,benzyldimethyltetradecylaluminum chloride, tributylmethylaluminumchloride, tetrabutylphosphinium tetrafluoroborate,1-butyl-1-methylpyrrolidium chloride, 1-butyl-3-methylimidazoliumtetrachloroaluminate, 1-butyl-4-methylpyridium chloride,1-butyl-4-methylpyridium tetrafluoroborate, and the like.

The water-based electrolyte may preferably include a cation representedby the following Chemical Formula 2 or 3 in order to have high ionconductivity and viscosity showing excellent electric properties:

[in Chemical Formula 2 or 3,

R¹ to R⁴ are each (C1-C20)alkyl, (C2-C20)alkenyl or (C2-C20)alkynyl,

wherein the alkyl, alkenyl and alkynyl may be further substituted withat least one selected from hydroxy, amino, —SO₃H, —COOH, (C1-C5)alkyl,(C1-C5)alkoxy, Si(R²¹)(R²²)(R²³)(R²¹, R²² and R²³ are each independentlyhydrogen or (C1-C5)alkyl, (C1-C5)alkoxy).]

More preferably, the water-based electrolyte may include at least onecompound selected from the following structures:

The water-based electrolyte may contain at least one lithium saltselected from a group consisting of LiPF₆, LiTFSI (Lithiumbis(fluorosulfonly)imide), LiBF₄, LiClO₄, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂,LiN(CF₃SO₂)₂, LiN(SO₃C₂F₅)₂, LiCF₃SO₃, LiC₄F₉SO₃, LiC₆H₅SO₃, LiSCN,LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein, x andy are each natural number), LiCl, LiI and LiB(C₂O₄)₂, wherein thelithium salt may be contained in a concentration of 0.025 to 1 mole inorder for produced Li₂O₂ to increase an ion conductivity withouthindering a continuous reaction on a surface of porous cathode.

In addition, an organic electrolyte contained in the separator 410 is anon-water-based electrolyte, wherein as the organic electrolyte, anorganic solvent not containing water may be used, and as thenon-water-based organic solvent, a carbonate-based solvent, anester-based solvent, an ether-based solvent, a ketone-based solvent, anorganosulfur-based solvent, an organophosphorous-based solvent or anaprotic solvent may be used.

As the carbonate-based solvent, dimethyl carbonate (DMC), diethylcarbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC),methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethylcarbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC),fluoroethylene carbonate (FEC), butylene carbonate (BC) and the like,may be used, and as the ester-based solvent, methyl acetate, ethylacetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone,caprolactone, and the like, may be used.

As the ether-based solvent, dibutyl ether, tetraglyme, diglyme,dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like,may be used, and as the ketone-based solvent, cyclohexanone, and thelike, may be used.

In addition, as the organosulfur-based solvent and theorganophosphorous-based solvent, methanesulfonyl chloride andp-trichloro-n-dichlorophosphorylmonophosphazene, and the like, may beused, and as the aprotic solvent, nitriles such as R′CN (R′ is C2 to C20hydrocarbon group having straight chain, branched, or cyclic structureand may include a double bond ring or an ether bond), and the like,amides such as dimethylformamide, and the like, dioxolanes such as1,3-dioxolane, and the like, sulfolanes, and the like, may be used.

The non-water-based organic solvent may be used alone or two or morethereof may be mixed, and a mixing ratio in the mixture of two or morethereof may be appropriately adjusted according to desired performanceof the battery, which may be appreciated by a person skilled in the art.

Here, the non-water-based organic solvent may contain a lithium salt,wherein the lithium salt may be dissolved into the organic solvent tofunction as a source of the lithium ion in the battery, and for example,the lithium salt serves to promote movement of the lithium ions betweenthe anode and the lithium ion conductive solid electrolyte 420.

The lithium salt may be the same as the lithium contained in thewater-based electrolyte or different from each other, and one or two ormore selected from a group consisting of LiPF₆, LiTFSI (Lithiumbis(fluorosulfonly)imide), LiBF₄, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂,Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein, x and y are eachnatural number), LiF, LiBr, LiCl, LiI and LiB(C₂O₄)₂(lithiumbis(oxalato)borate; LiBOB) may be used as the lithium salt.

The lithium salt may have a concentration of 0.1 to 2.0 mole. In thecase in which the lithium salt has the above-described range ofconcentration, the electrolyte has an appropriate conductivity andviscosity, such that excellent electrolyte performance may be shown, andthe lithium ions may be effectively moved. The non-water-based organicsolvent may further contain other metal salts such as AlCl₃, MgCl₂,NaCl, KCl, NaBr, KBr, CaCl₂, and the like, in addition to the lithiumsalt.

The solid electrolyte 420 may indicate a lithium ion conductive solidelectrolyte film and may function as a protective film so that watercontained in the water-based electrolyte is not directly reacted withlithium contained in the anode. Examples of the lithium ion conductivesolid electrolyte 420 may include a lithium ion conductive glass, alithium ion conductive crystal (ceramic or glass-ceramic) or aninorganic material containing a mixture thereof, and the like.

Hereinafter, the present invention will be more appreciated by thefollowing drawings and examples, which are given by way of illustrationbut are not intended to limit the protective scope defined by theattached claims of the present invention.

[Preparation Example 1] Preparation of Nafion Coated Air-Cathode

Hot Pressing Method Using Nafion Membrane

Nafion perfluorinated membrane (N-115 or N-117, Sigma-Aldrich) was cutusing punch so as to be slightly larger than a diameter of air-cathode(for example, in a case of air-cathode having a diameter of 1.5 cm,Nafion perfluorinated membrane has a diameter of 1.7 cm). A platinum(Pt) catalyst layer of air-cathode was sequentially stacked on theNafion membrane while contacting to each other, and put into a releasefilm bag. The prepared release film bag was maintained under a pressureof 100 kg/cm² for 3 minutes using hot press. Here, the hot press wasmaintained at a temperature of 135° C. Here, in order to induce changein microstructure of air-cathode, pressure, temperature, and retentiontime may be changed.

Dip Coating Method Using Nafion Resin Solution

Nafion perfluorinated resin, aqueous dispersion (10 wt % in H₂O,Sigma-Aldrich) was put into a Petri dish in an appropriate amount (100mL in a case of air-cathode having a diameter of 1.5 cm) according to asize of the air-cathode, and then, maintained for 5 to 10 minutes in astate in which the platinum (Pt) layer of the air-cathode was completelyimmersed thereinto. Next, the reactant was dried under laminar flow in afume hood at room temperature for 24 hours. As the Nafion resin used inthe present Preparation Example 1, a resin solution having a highconcentration (for example, 30 wt % in H₂O) may be used, and the dippingand drying processes may be repeated 1 to 2 times or a plurality oftimes according to thickness of the Nafion film and microstructure forfinally producing the platinum catalyst layer of the air-cathode.

[Preparation Example 2] Preparation of Microporous Polyolefin-BasedComposite Film (or Separator)

The microporous polyolefin-based composite film (or separator) used tosuppress evaporation of the electrolyte in the lithium air battery is aporous film containing a polymer binder and an inorganic particle,wherein as the polymer binder, water-soluble polymer and non-solublepolymer are simultaneously used, and the contents thereof are adjustedto enable optimization of heat resistance, adhesive strength, andmoisture content.

Preparation Method 1

In order to prepare a microporous polyolefin-based film, high densitypolyethylene having a weight average molecular weight of 3.8×10⁵ wasused. As diluent, dibutyl phthalate and paraffin oil having a 40kinematic viscosity of 160 cSt were mixed at 1:2 ratio to be used,wherein the content of polyethylene and the diluent were 30 wt %, and 70wt %, respectively. The composition was pressed out at 240° C. using abiaxial compound having T-die mounted thereon and passed through asection set at 170° C., thereby inducing phase-separation ofpolyethylene and diluent present in a single phase, and then, a sheetwas prepared using casting roll. The sheet prepared using a successivebiaxial stretching machine was stretched at a stretching temperature of128° C. by six times, in a longitudinal direction and a transversedirection, respectively, and after being stretched, a heat settingtemperature was 128° C., and a heat setting width was 1-1.2-1.1. A finalthickness of the prepared microporous polyethylene-based film was 16 μm,gas permeability (Gurley) was 130 sec, and a void closing temperaturewas 140° C.

The microporous polyolefin-based film prepared by the above-describedmethod was used, 2.6 wt % of polyvinylalcohol having a meltingtemperature of 220° C. and a saponification degree of 98%, acrylic latexhaving Tg of −45° C. in a solid content of 3.1 wt % (Rovene 6050), and47 wt % of Al₂O₃ (an average particle size of 0.4 μm) powder weredissolved into deionized water. The thus-prepared reactant was appliedonto a cross-section of the microporous polyolefin-based film using adie coating scheme, a solvent was removed and dried by applying apredetermined air volume in an oven at 60° C., thereby finally preparingthe microporous polyolefin-based composite film including a coatinglayer having a thickness of 4.2 um.

A photograph showing a surface of the microporous polyolefin-basedcomposite film prepared by the above-described method was shown in FIG.9 and a photograph showing a cross section thereof was shown in FIG. 10.

Preparation Method 2

In order to prepare a microporous polyolefin-based film, high densitypolyethylene having a weight average molecular weight of 3.8×10⁵ wasused, and as diluent, dibutyl phthalate and paraffin oil having a 40kinematic viscosity of 160 cSt were mixed at 1:2 ratio to be used,wherein the content of polyethylene and the diluent were 25 wt %, and 75wt %, respectively. The composition was pressed out at 240° C. using abiaxial compound having T-die mounted thereon and passed through asection set at 170° C., thereby inducing phase-separation ofpolyethylene and diluent present in a single phase, and then, a sheetwas prepared using casting roll. The sheet prepared using a successivebiaxial stretching machine was stretched at a stretching temperature of128° C. by seven times, in a longitudinal direction and a transversedirection, respectively, and after being stretched, a heat settingtemperature was 126° C., and a heat setting width was 1-1.2-1.2. A finalthickness of the prepared microporous polyethylene-based film was 9 μm,gas permeability (Gurley) was 110 sec, and a void closing temperaturewas 139° C.

To the microporous polyolefin-based film as described above, 0.5 wt % ofSilanol-polyvinylalcohol copolymer having a melting temperature of 225°C. and a saponification degree of 97.5% and 1.5 wt % (Rovene 4305) ofcarboxylated Stylene butadiene Latex having Tg of −24° C. were used, and22 wt % of plate-shaped Al₂O₃ (average particle size of 1.5 μm) powderhaving an aspect ratio of 10 to 20 was dissolved into deionized water tobe prepared. The thus-prepared reactant was applied onto a cross-sectionof the microporous polyolefin-based film using a micro-gravure coatingscheme, a solvent was removed and dried by applying a predetermined airvolume in an oven at 60° C., thereby finally preparing the microporouspolyolefin-based composite film including a coating layer having athickness of 3.5 um.

Preparation Method 3

The microporous polyolefin-based film prepared by the above-describedPreparation Method 1 was used, 0.6 wt % of polyvinylalcohol having amelting temperature of 220° C. and a saponification degree of 99% andacrylic latex having Tg of −45° C. in a solid content of 4.0 wt %(Rovene 6050) were used, and 40 wt % of Al₂O₃ (an average particle sizeof 0.6 μm) powder was dissolved into deionized water. The thus-preparedreactant was applied onto a cross-section of the microporouspolyolefin-based film using a die coating scheme, a solvent was removedand dried by applying a predetermined air volume in an oven at 60° C.,thereby finally preparing the microporous polyolefin-based compositefilm including a coating layer having a thickness of 2.5 um.

[Example 1] Preparation of Lithium Air Battery

16.3 g of LiCH₃COOH (lithium acetic acid, molar mass=102.02 g/mol,Sigma-Aldrich), 6.8 g of LiCl (lithium chloride, molar mass=42.39 g/mol,Sigma-Aldrich), and 3.8 g of LiOH (lithium hydroxide, molar mass=23.95g/mol, Sigma-Aldrich) were dissolved into 1 liter (L) of D.I. water,thereby preparing water-based electrolyte having a concentration of 1M,respectively, as a second electrolyte. A lithium metal thin film wasused as an anode, and polypropylene (SKI, F305CHP, 525HV) was used as aseparator disposed on the lithium metal thin film. As a porousair-cathode, Nafion coated air-cathode was prepared according toPreparation Example 1 above. As a basic air-cathode, a gas diffusionlayer having a platinum catalyst layer (Pt 10 wt %, Fuel Earth, EP1019)was used. The microporous polyolefin-based composite film (SKI, F305CHP,525HV) used in order to suppress evaporation of the electrolyte wasprepared by Preparation Example 2 above.

The anode, which is the lithium metal thin film, was installed in astainless case, and a separator prepared by injecting one oforganic-based electrolytes (1M of LiTFSi in EC:DMC=1:1, 1M of LiTFSi inEC:PC=1:1, 1M of LiPF₆ in EC:DEC=1:1) thereto was positioned at a sidefacing the anode, and a solid electrolyte film (OHARA, AG-01) wasmounted thereon, and the accommodation body into which the preparedwater-based electrolyte was injected was installed on the solidelectrolyte film, such that the anode and the cathode faced each other.Then, a carbon paper washer was disposed on the cathode, and the secondhousing 120 was pressed out to fix the cell, thereby manufacturing alithium air battery. 1M LiCH₃COOH in D.I water was used as thewater-based electrolyte, 1M LiTFSi in EC:DMC=1:1 having wettability withthe separator was used as the organic-based electrolyte, and othermaterials were used as the same as described above.

In order to evaluate charge and discharge properties of the lithium airbattery manufactured by the above-described method, the battery wascharged and discharged in a constant current mode of 0.25 mA/cm² under atemperature of 25° C., a pressure of 1 atm, for a predetermined time,which is 24 minutes.

Example 2

Example 2 was conducted for comparison between a case of suppressingevaporation of the water-based electrolyte using the microporouspolyolefin-based film in Example 1 above and a case of not suppressingevaporation thereof. In addition, in order to clearly show thecomparison, a microporous air-cathode to which Nafion film was notapplied was used, and charge and discharge properties of the lithium airbattery were evaluated by flowing 5 to 10 ccm of pure O₂ gas (relativehumidity 0%) having moisture of 0.6 ppm or less rather than an ambientair, through ventilation holes 121 of the lithium air battery. Resultsobtained from the charge and discharge test were shown in FIGS. 11 and12 and Table 4. Life span of the lithium air battery manufactured byapplying the microporous polyolefin-based film to air-cathode wasremarkably improved.

TABLE 4 Unit Capacitance of Charge and Microporous Polyolefin- DischargeCycle Running Time based Film 0.18 mAh 7  7 (H):45 (M):43 (S)Non-Applied 0.18 mAh 52 58 (H):55 (M):47 (S) Applied

Example 3

A lithium air battery of Example 3 was manufactured by preparingair-cathode obtained by using N-117 Nafion membrane of Example 1 above,performing Nafion coating with hot pressing method of PreparationExample 1, and applying the microporous polyolefin-based film thereto.After the charge and discharge of two lithium air batteries (sample 1and sample 2) were repeated 50 times, change in charge and dischargeenergy and efficiency of charge and discharge energy were shown in FIGS.13 to 18, and discharge energy retention rate was shown in Tables 5 and6. It could be appreciated that the air-cathode to which Nafion membranewas applied showed stable and excellent performance of the battery. Inaddition, as shown in FIG. 19, in a case of applying Nafion coating tothe air-cathode, the platinum (Pt) catalyst layer was completely blockedfrom being slowly detached, such that after 50 cycle of the charge anddischarge of the battery, discoloration of the second electrolyte (orthe water-based electrolyte) due to the detached platinum (Pt) catalystlayer did not completely occur.

TABLE 5 Sample 1: Discharge Energy Retention Rate after 50 CyclesDischarge Energy [mWHr] Cycle Discharge Energy Retention Rate [%] 0.54 1103.7 0.56 50

TABLE 6 Sample 2: Discharge Energy Retention Rate after 50 CyclesDischarge Energy [mWHr] Cycle Discharge Energy Retention Rate [%] 0.55 198.1 0.54 50

Example 4

A lithium air battery of Example 4 was manufactured by preparingair-cathode obtained by performing Nafion coating with the dip coatingmethod of Preparation Example 1 in Example 1, and applying themicroporous polyolefin-based film thereto. After the charge anddischarge of the lithium air battery was conducted 421 times, change incharge and discharge energy and efficiency of charge and dischargeenergy were shown in FIGS. 20 to 22, and a discharge energy retentionrate after conducting 421 cycles was shown in the following Table 7. Thebattery applied by Nafion dip coating scheme had excellent batteryperformance, in particular, significantly excellent cycle life span.

TABLE 7 Discharge Energy Retention Rate after 421 Cycles DischargeEnergy [mWHr] Cycle Discharge Energy Retention Rate [%] 0.55 1 85.5 0.47421

It may be appreciated from the lithium air batteries according toExamples 1 to 4 of the present invention that the Nafion coating mayprevent the platinum (Pt) catalyst layer from being slowly detached andthe microporous polyolefin-based film may prevent the water-basedelectrolyte solvent from being evaporated, thereby significantlyimproving the performance of the battery. It may be appreciated thatexcellent life span cycle which is 421 cycles under an atmosphericcondition may be secured, and discharge energy retention rate may alsobe significantly high.

In addition, in the case in which lithium metal is used as the anode,due to an effect of moisture, life span over several tens of cycles maynot be secured in the existing lithium air battery. However, the lithiumair battery according to the present invention may prevent an electricshort circuit due to a structure thereof and basically obstructinfiltration of moisture, thereby securing excellent life span cycle.

Further, in a case of using an ionic liquid as a water-based electrolytein the lithium air battery according to the present invention, inparticular, using the ionic liquid having anions such as FSI or TFSI asthe water-based electrolyte, deterioration due to decomposition reactionwith lithium may be reduced, such that excellent charge and dischargeproperties may be provided. Here, even in a case of a general half-cell,at least 4 to 12 hours stabilization time is required, meanwhile, thelithium air battery according to the present invention has a shortstabilization time of 30 minutes to 1 hour.

With the lithium air battery according to the present invention, thecathode contacting the electrolyte and using oxygen in the air as theactive material is coupled to the hydrophobic microporouspolyolefin-based film and the membrane through which the lithium ionspass, such that even though the charge and discharge of the battery isrepeated, the catalyst layer may not be detached, but the water-basedelectrolyte solvent may be prevented from being evaporated, therebypreventing performance deterioration due to repetition of the charge anddischarge of the lithium air battery, and extending life span.

The present invention is not limited to the above-mentioned embodimentsbut may be variously applied. In addition, it will be appreciated bythose skilled in the art that various modifications and changes may bemade without departing from the appended claims of the presentinvention.

What is claimed is:
 1. A lithium air battery comprising: a first electrode part including a lithium metal; a second electrode part disposed spaced apart from the first electrode part, the second electrode part including a gas diffusion layer one side of which contacts an air, a single catalyst layer formed at an other side of the gas diffusion layer, the single catalyst layer being formed of a mixture of platinum, a binder, and optionally a conductive material, a porous membrane made of a polyperfluorosulfonic acid (PFSA) resin closely adhered to the single catalyst layer so that lithium ions pass therethrough, and a microporous polyolefin-based composite film formed on the one side of the gas diffusion layer, the microporous polyolefin-based composite film including a microporous polyolefin-based film and a coating layer formed on the microporous polyolefin-based film, the coating layer containing a water-soluble polymer binder, a water-non-soluble polymer binder and an inorganic particle; and an electrolyte part provided between the first electrode part and the second electrode part, wherein the electrolyte part includes a separator one side of which is closely adhered on the first electrode part and containing an organic-based electrolyte, a solid electrolyte closely adhered on an other side of the separator, and a water-based electrolyte provided between the solid electrolyte and the membrane, wherein the microporous polyolefin-based composite film, the gas diffusion layer, the single catalyst layer, and the membrane are sequentially stacked, such that the microporous polyolefin-based composite film is disposed to contact an air and the membrane is disposed to contact the water-based electrolyte, and wherein the single catalyst layer is directly contacted with the gas diffusion layer and the membrane.
 2. The lithium air battery of claim 1, further comprising: a housing part including a first housing provided with a space part having an open upper side, and a second housing having an air accommodation part disposed at an upper portion of the first housing, sealing the space part of the first housing, and having an open lower side, and ventilation holes formed therein to communicate with the air accommodation part, wherein the first electrode part is accommodated into the space part of the first housing, the second electrode part is coupled to a lower side of the air accommodation part of the second housing to be spaced apart from the first electrode part, and the electrolyte part is provided in the space part of the first housing to be provided between the first electrode part and the second electrode part.
 3. The lithium air battery of claim 2, wherein an accommodation body is provided on an upper side of the solid electrolyte and includes an accommodation hole vertically penetrating therethrough, and the accommodation body is disposed so that the solid electrolyte, the separator, and the first electrode part are closely adhered to one another in the space part.
 4. The lithium air battery of claim 2, wherein the housing part further includes a third housing interposed between the first housing and the second housing and having a fixing hole vertically penetrating therethrough so that the second electrode part is fixed to the fixing hole.
 5. The lithium air battery of claim 1, wherein the porous membrane is closely adhered to the single catalyst layer by heating and pressing the PFSA resin or by a dip-coating method using a PFSA resin solution.
 6. The lithium air battery of claim 1, wherein the gas diffusion layer comprises carbon paper. 